1. Field of the Invention
The present invention relates to a coil block and an electronic device using the same. More particularly, the present invention relates to a coil block and an electronic device using the same, which can provide an inductance component to an element that requires inductance.
2. Description of the Related Art
Generally, an LC filter used in a digital amplifier includes a coil L and a capacitor C. This coil, as shown in FIG. 2A, is composed of a core and a wiring, and is connected in series to outputs Out+ and Out− of the digital amplifier. The capacitor, as shown in FIGS. 2B and 2C, is composed of a capacitor C1 positioned at both ends of two coils and a capacitor C2 positioned between one of the coils and ground.
In addition, the LC filter used at the output terminals of the digital amplifier serves to restore to the original signal by low-pass-filtering high-band components of a pulse width modulation (PWM) signal. Here, at shown in FIG. 1A, the PWM signal can be expressed as a difference between two positive (+) and negative (−) signals, and the magnitude of the original signal can be indicated using the difference in pulse width between the two signals. If the magnitude of the original signal is varied, the pulse width of the PWM signal is simultaneously varied, in various ways as shown in FIGS. 1A, 1B, and 1C, according to its PWM modulation method.
In this case, if the PWM signal always has an inversed phase structure as shown in FIG. 1A, a common coil, where two windings are wound on to one core in a direction in which magnetic forces of the two windings overlap each other, may be used as shown in FIG. 2A.
If current flows in different directions through the two windings that are wound on to one core in the common coil as shown in FIG. 2A, magnetic forces having the same direction are produced through the windings, so that the coil performs a normal operation, which is a well known technology.
In this case, the inductance value L for one coil is in proportion to the square of the number of turns of the windings as shown in Equation (1), and thus if it is assumed that the number of turns of one winding in the common coil is n, the total number of turns for current flow becomes 2n. Thus, if it is assumed that the respective inductance of the common coil is L, the whole inductance of the coil becomes 4L . Accordingly, if the common coil having the individual inductance value of L, as shown in FIGS. 2B and 2C, is used, it has the effect of using two general coils having the inductance of 2L.L=μ0n2Al   (1)
Here, μ0 denotes a magnetic permeability, n the number of turns, and Al the volume of the coil, respectively.
On the other hand, if the PWM signal has both an inversed phase component and a same phase component as shown in FIGS. 2B and 2C, current flows in the same direction as the current flow through the two coils at a point of the same phase where the current flows in the same direction through the two windings, as shown in FIG. 2D.
In this case, since the two windings are wound in the same direction, the directions of the magnetic forces thereof become opposite to each other. Accordingly, the magnetic forces offset each other, resulting in that the inductance of the coil becomes “0”. If the inductance of the coil becomes “0”, a direct charging/discharging of a capacitor C2 is performed to cause the occurrence of a transient phenomenon due to overcurrent. If the capacitor C2 is removed, the transient phenomenon does not occur any more, but the PWM component of the same phase is not removed to cause a noise component not to be cut off.
In addition, although coils used in an LC filter are passive elements, they are large-sized and expensive, unlike resistors and capacitors, developers' dissatisfaction has been increased. Accordingly, developers of digital amplifiers have continuously made an investment in reduction of the size of coils, and have introduced a common coil as the result. In an early stage of digital amplifiers, PWM signal had an inversed phase only, and thus the common coil was satisfactorily used. However, with the development of technology, digital amplifiers, which use a PWM method that has components of the same phase to achieve more efficient control, have been increasingly used. In this case, since two general coils should be separately used instead of the common coil, damage rather occurs in size and cost of the digital amplifier.